Release of transmitter from spinal cord (SC) and dorsal root ganglion (DRG) cells in cell culture is better described by binomial than by Poisson statistics, indicating that the probability of transmitter release is relatively high for each release element. The statistically defined release element corresponds to the individual synaptic bouton. Catecholaminergic connections between locus coeruleus explants and dissociated spinal cord neuron are predominantly depolarizing, alpha receptor mediated, and are due to a decrease in neuronal membrane conductance, which results in a large increase in excitability. Polyneuronal innervation of muscle by neuroblastoma x glioma hybrid cells is decreased by veratridine activation of the cells. Specific developmental periods have been found during which spinal cord cells are sensitive to tetrodotoxin (TTX) induced inactivity. The degree and age dependency of this effect varies with the neuronal marker used. In addition, our data suggest the existence of a trophic factor which prevents TTX toxicity. Combined radioautography and immunohistochemistry of cerebral cortical neurons in cell culture have shown that 3H-GABA accumulating neurons are those which contain immunoreactive glutamate decarboxylase (GAD), the GABA-synthesizing enzyme.